Continuing research on this project is concerned with the elucidation of hormonal mechanisms controlling membrane permeability and transport processes at the cellular and molecular levels. Within this general framework we are investigating (1) the effect of changes in primary chemical structure on the topochemistry and biological activities of selected neurohypophyseal peptides, (2) the nature of intermediate events and the final effector process in the action of peptide hormones and (3) the phenomena associated with modulation and termination of hormone action.